Vaginal microbicides are compounds applied to the inside of the vagina that may protect women against vaginal transmission of HIV and other STIs. This study will evaluate the safety of the vaginal microbicide UC-781. Studies have shown UC-781 to be an effective inhibitor of HIV-1 reverse transcriptase. UC-781 has been tested in animal models and in Phase I and II studies in humans. The results of these studies indicated that cervical tissue was fully protected from different variants of HIV. The purpose of this study is to assess the incidence of epithelial disruption and inflammation in the cervix, vagina, and vulva of healthy HIV uninfected women after a single exposure to UC-781 vaginal gel. This study will compare the results of leaving the microbicide in the vagina for varying lengths of time.